The European Commission said on Monday that low-cost carrier Ryanair (RYAAY) must comply with EU regulations on passenger rights regarding its cancellations of flights during a six-week period, the Financial Times reports.

The Commission added that Ryanair might have to reimburse and compensate passengers for the cancellations of between 40 and 50 flights per day until the end of October.

Ryanair has warned that the penalties could amount to 20 million euros (about $23.9 million) in compensation.

"Airlines operating in the EU need to respect the European rules.... Passengers whose flights are cancelled have a comprehensive set of rights," a Commission spokesman said.

"We have to check if all this is respected by Ryanair. For instance, you are entitled to reimbursement if you are not warned two weeks in advance," he added.